#include <bits/stdc++.h>
using namespace std;
#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define REP(i,n) FOR(i,0,n)
#define ALL(v) begin(v),end(v)
template<typename A, typename B> inline bool chmax(A & a, const B & b) { if (a < b) { a = b; return true; } return false; }
template<typename A, typename B> inline bool chmin(A & a, const B & b) { if (a > b) { a = b; return true; } return false; }
using ll = long long;
using pii = pair<int, int>;
constexpr ll INF = 1ll<<30;
constexpr ll longINF = 1ll<<60;
constexpr ll MOD = 1000000007;
constexpr bool debug = false;
//---------------------------------//

int main() {
	double a, b;
	cin >> a >> b;
	
	constexpr int div = 10000000;
	const double dx = (b - a) / div;
	const double pi = acos(-1);
	double ans = 0;
	REP(i, div) {
		const double m = dx * i + a;
		ans += 2 * pi * sqrt(1 - m * m) * dx * 1.2732395443360573;
	}
	printf("%.16f\n", ans);
}